iio/adc: ingenic: add JZ4760 support to the sadc driver

The jz4760 sadc is very similar to the jz4770 one, but has a VREF of 2.5V
and 3 aux channels.

modify ingenic_adc_read_chan_info_raw() needs a change to account for it.

Signed-off-by: Christophe Branchereau <cbranchereau@gmail.com>

Reviewed-by: Paul Cercueil <paul@crapouillou.net>
Link: https://lore.kernel.org/r/20210726082033.351533-4-cbranchereau@gmail.com


Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>